The present invention relates to LED driver circuits, and particularly, to an LED driver circuit incorporating automatic on and off control based on ambient light sensing.
Automatic on and off control of lighting based on ambient light sensing is advantageous in providing desired light switching in applications such as emergency back-up lighting and dusk-to-dawn security or architectural lighting. One prior art design for a light driver includes driver integrated circuits providing the required light supply signals and a microcontroller to provide control logic and other functionality required for driving the lights. An I/O port of the microcontroller is coupled to a luminous detection circuit, including a cadmium sensor, a photo diode, or a phototransistor, and provides on and off control of the light depending on the ambient light detected by the luminance detection circuit.
One type of driver circuit for LED lighting utilizes a power factor correction (PFC) controller, for example, a current-mode PFC controller operating in transition mode, and a flyback converter providing an isolated, low cost, low component count voltage to LEDs. Such PFC controllers packaged as an integrated circuit can include a monitor/disable input used to detect and provide protection, for example, from overvoltage of the PFC pre-regulator and/or feedback failure. An exemplary monitor/disable input operates as an output voltage monitor and disables the controller if the voltage drops below a particular threshold, thus providing the potential for on and off control via a voltage control signal.
It is desirable to provide on and off control of an LED driver circuit utilizing a PFC controller based on ambient light detection without having to increase the integrated circuit part count and cost of implementing typical control schemes disclosed by the prior art, such as the inclusion of a microcontroller providing I/O ports and logic to support such on and off control.